The present invention relates generally to extensile and retractile bellows structures.
It is common practice in the prior art to utilize extensile and retractile bellows structures to provide a protective cover in mechanical arrangements which may be exemplified by a moving rod operatively associated with a fixed cylinder or other guiding outer member, for the purpose of protecting the relatively movable parts against dirt, dust, fumes, moisture, or the like. Such bellows have also been utilized to seal in lubricants, fluids and other media. In the use of well known accordian types of bellows in organizations, where the ends are in sealed relation to the associated relatively movable parts, a problem is presented in that the extensile and retractile movements have a tendency to produce a pumping action on the media due to volume and pressure changes within the bellows interior. This pumping action is undesirable in many installations, since the pressure increase within the bellows has the effect of providing a spring loading which can interfere with the operation of the mechanism.
In order to alleviate the pressure problem in the bellows, various arrangements have been tried for venting the bellows interior. Such arrangements are shown in the U.S. Pats. of Johnston, No. 3,186,722 and Hines, No. 3,369,411. Venting arrangements are relatively costly and tend to reduce the beneficial effects produced by the bellows. For example, when the bellows is vented to the surrounding environment, the outlet must necessarily be equipped with a fine filter or other means to prevent dust from entering the interior of the bellows. It will be appreciated, that the venting solution is not adaptable to installations in which lubricants or other media must be contained, without loss, in the bellows.
In other venting arrangements, as shown in the prior art, attempts have been made to solve the problem by venting air into a much larger rigid receptacle in the case of oil well pumping equipment. However, these arrangements are complicated and of a size which prevents their employment under confined operating conditions in small devices such as push-pull cables and the like.
Another known solution is illustrated in U.S. Pat. of Wasley, No. 2,960,372, which uses a double-ended device and transfers the compressed media at one end through a passage to the expanding opposite end. Where the ends are remotely positioned, it becomes necessary to utilize connecting pipe lines or tubing which are of considerable length and cause porting problems. Thus, the transfer of fluid media from one bellows to the other is, as a practical matter, only possible when the distances are relatively short and the passages relatively large. Such a method is not readily adaptable for use in push-pull cable arrangements having limited clearances.
The present invention effectively solves the prior art problem by providing a single bellows structure which is pressure compensated and requires no venting connections.